The present invention relates to an electrofusion coupler for use in joining together plastic pipes, wherein the coupler includes a welding socket which is adapted to receive the ends of the pipes to be joined together with a close fit and which incorporates coils of resistance wires or filaments which when energized cause the material in the welding socket to fuse together with the material in the pipe walls at the positions of said coils.
Couplers of this kind are used generally in joining together plastic pipes and in connecting plastic pipes to pipe bends, T-pieces and the like. The welding sockets are usually provided with inwardly projecting shoulders in their center regions and incorporate a resistance coil on each side of the shoulders. When joining two pipes together, the pipe ends can be inserted into the socket until stopped by the shoulders. The person coupling the pipes will then know that the pipes have been centered correctly in the socket. A voltage source is then connected to the coils. The material in the inner surface of the socket and in contact with the material at the pipe ends will therewith fuse together locally as a result of the heat generated in the resistance wires.
This represents a very simple and effective method of joining together simple pipe conduits. Many installation, for instance gasoline transporting installations, require the use of double conduits, i.e. conduits which include two coaxial pipes and which are constructed so as to provide an annular space between the radially inner and the radially outer pipe. This space is used to detect any leakage that may occur in the inner or the outer pipe, in addition to enhancing safety against leakage onto the surrounding ground. To this end, the space contains a gas, suitably air, that has a pressure in excess of or below the ambient pressure. The occurrence of a leakage can be detected, by monitoring the pressure in said space. It is important that pressure changes in the space between the pipes are able to propagate along the full length of a monitoring zone in a conduit system or pipework. When joining such pipes, the inner pipe must be joined per se and the outer pipe must be joined per se, such that communication is also obtained between the annular spaces in the mutually joined double conduits.
When using conventional couplers of the aforedescribed kind to effect such joins, it is first necessary to join the inner pipes together with the aid of a fusion welding socket that is fused together with the pipes in a first fusing operation. Prior to this, it is necessary to first place a cross-section reducing socket on each pipe end, these sockets each having a part into which the outer pipe tightly fits and a part of larger diameter which will accommodate the inner fusion welding socket for the inner pipes. These reduction sockets are intended to be joined with the aid of an outer welding socket of larger diameter. It is also necessary to push this outer socket onto a pipe end prior to welding the inner pipes together. The reduction sockets and the outer welding socket must then be welded together with respective outer pipes and with each other in a second welding operation.
A greater number of components and working operations are required in the case of T-couplings for instance. The use of such conventional fusion welding sockets in joining together double-pipe conduits is thus expensive because of the large number of components that must be used and because several welding operations must be carried out sequentially. Especially the division of the pipe welding into different working operations is time consuming.
A primary object of the present invention is to provide a technique which greatly simplifies the work of joining together double-pipe conduits.
In this regard, one object is to join together double-pipe conduits with the aid of one single fusion welding coupler.
Another object is to enable all welding operations to be carried out simultaneously when joining a T-coupling.
The invention is based on the realization that these objects can be achieved with the aid of a fusion coupler or welding socket that includes parts of mutually different diameters which will fit around the outer pipe and the inner pipe respectively of a double-pipe conduit, and which includes passageways that provide communication between the annular spaces of two double-pipe conduits joined together with the aid of the welding socket.
Reference in the following and in the claims to a pipe coupling and pipe joining operation implies joining together two double-pipe conduits and joining of one such conduit to a joint piece, a pipe bend, a T-coupling and the like that include double-pipes or pipes provided with passageways in the walls thereof with the intention of providing requisite communication with the space between the pipes in a double-pipe conduit.
The particular characteristic features of a fusion coupler of the kind defined in the first paragraph are that the welding socket has a larger diameter at its ends than along an intermediate part thereof, that the diameter at said ends is adapted to receive an outer pipe with a close fit and the diameter along said intermediate part is adapted to receive with a close fit an inner pipe of a double-pipe conduit that includes two coaxial pipes and a leakage detection space between said pipes, that the socket includes heating coils of resistance wires or filaments that when energized function to locally fuse the socket material with the material of both the outer pipes and the inner pipes in two double-pipe conduits to be joined together with the aid of the fusion welding socket, and that the fusion welding socket includes at least one passageway which interconnects the spaces in the socket on both sides of the intermediate part.
A fusion welding socket of this kind enables, for instance, two double-pipe conduits to be joined together with the aid of one single component and also enables all necessary fusion welding operations to be carried out in one s ingle step, by connecting an outer voltage source to two terminals on the socket. This greatly facilitates the work that is entailed in joining together double-pipe conduits, and also makes the work less expensive. Furthermore, the use of a single welding socket also enables a check to be made as to whether or not the inner pipe has been welded correctly, from outside the conduit.
Further characteristics of the invent ion will be apparent from the dependent claims.